1. Field of the Invention
The invention concerns a monitoring procedure and a monitoring installation for numerically-controlled machine tools with a motor-rotated work spindle and a separating protection device.
2. Discussion of Related Art
For the protection of the operator, numerically controlled machine tools are as a rule, equipped with partitions or protective booths which are intended to prevent potential danger to the operator from flying tools, work or fragments. It is, however, the inspection windows of such partitions or protective booths which are of a limited strength. Since protective devices must often be mobile, their thickness also has limits. Due to incorrect programming or faulty operation of the machine tools, operating conditions may intervene which can lead to danger for operators. Thus, for example, a replaceable bezel of a milling cutter may, in the event of a fracture due to incorrect programming or incorrect input of the rotational speed, fly away from the tool holder with such high energy that the separating protection devices cannot withstand the impact.
It is a primary purpose of the present invention to provide a monitoring procedure and a monitoring installation for machine tools which make possible an improvement in machine safety.
According to the invention, the actual mass inertia moment of a tool held in the work spindle is determined on the basis of a measurement and compared with a mass inertia moment calculated from the predetermined data for the tool in question. In this way it is possible to verify whether the geometrical tool data entered into the NC control agree with the data of the tool fitted into the work spindle or whether, for instance, erroneous diameter values were entered or programmed. By comparing a predetermined parameter of the fitted tool with the maximum parameter which depends on the strength of the separating protective device with the chosen processing data, it is possible to determine whether the safety device could withstand a possible collision with flying parts. Rotation of the work spindle will only take place at the desired speed of rotation, if the actual mass inertia moment agrees with the calculated mass inertia moment and the predetermined parameter is smaller than or equal to the predetermined maximum parameter predetermined by the strength of the protection device. In this way it is possible to identify an erroneous tool diameter and speed of rotation entry, and the speed of rotation of the work spindle can be restricted to an admissible value or the work spindle can be stopped and an error message issued.
Thus, for example, the predetermined parameter can advantageously be the entered tool diameter, which is compared with a maximum diameter dependent on the programmed speed of rotation. The predetermined parameter can, however, also be the entered desired speed of rotation of the work spindle, which is compared with a maximum speed of rotation dependent on the tool diameter.
In the event of a divergence between the actual mass inertia moment and the calculated mass inertia moment, or if the maximum parameter is exceeded, or both, it is advantageous to stop the work spindle drive or for an error message to be issued, or both. The speed of rotation of the work spindle can also be reduced to an admissible value.
The actual mass inertia moment of the tool fitted into work spindle can be calculated particularly easily on the basis of the acceleration time which is measured during the acceleration of the rotation speed of the tool to a predetermined reference value. If the machine tool possesses, for example, a mechanical or an optical system for determining the measurements of the tool fitted into the work spindle, the actual mass inertia moment can also be calculated from the tool data determined as set out above and compared with the mass inertia moment calculated from the entered values of the mass inertia moment. The actual mass inertia moment can also be calculated by either method, with a resulting greater degree of reliability.
In a further advantageous embodiment of the present invention, the work spindle is first accelerated to the predetermined reference speed of rotation while the current uptake of the drive motor is measured. By comparing the current uptake with a reference value obtained during the acceleration of a work spindle without a tool fitted, it is possible to verify whether a tool has been fitted into the work spindle. If this is not the case, the drive can be stopped and an error message issued.
A further advantageous embodiment is characterized by the fact that the work spindle will be driven at the predetermined desired speed of rotation only if an imbalance measured during the acceleration of the speed of rotation of the work spindle to a predetermined measured speed of rotation reference value is below a maximum admissible imbalance.